Electrolytic electrophotography

ABSTRACT

AN ELECTROLYTIC ELECTROPHOTOGRAPHIC PROCESS INVOLVING THE STEPS OF EXPOSING A PHOTOCONDUCTIVE LAYER COMPRISING A PHOTOCONDUCTIVE MATERIAL AND A BINDER FORMED ON AN ELECTRICALLY CONDUCTIVE BASE PLATE TO FORM THEREIN A LATENT IMAGE DUE TO THE DIFFERENCE IN ELECTRIC CONDUCTIVITY, AND SUBJECTING THE PHOTOCONDUCTIVE LAYER HAVING THE LATENT IMAGE TO ELECTROLYSIS IN AN ELECTROLYTE BATH TO FORM VISIBLE IMAGES ON THE LAYER, THE IMPROVEMENT WHICH COMPRISES FORMING A LAYER OF A DISPERSION OF A PIGMENT IN A FATTY OIL ON SAID PHOTOCONDUCTIVE LAYER BEFORE OR DIRECTLY AFTER EXPOSURE, SAID FATTY OIL BEING AT LEAST PARTIALLY LIQUID AT A TEMPERATURE OF FROM NORMAL TEMPERTURE TO ABOUT 40*C.

United States Patent O 3,565,613 ELECTROLYTIC ELECT ROPHOTOGRAPHY Yasuo Tamai and Masaaki Takimoto, Saitama, Japan, assignors to Fuji Photo Film Co., Ltd., Ashigara-Kamigun, Kanagawa, Japan No Drawing. Filed Dec. 6, 1967, Ser. No. 688,306 Claims priority, application Japan, Dec. 7, 1966, 41/ 80,246 Int. Cl. G03g 5/00 US. Cl. 96-1 4 Claims ABSTRACT OF THE DISCLOSURE An electrolytic electrophotographic process involving the steps of exposing a photoconductive layer comprising a photoconductive material and a binder formed on an electrically conductive base plate to form therein a latent image due to the difference in electric conductivity, and subjecting the photoconductive layer having the latent image to electrolysis in an electrolyte bath to form visible images on the layer, the improvement which comprises forming a layer of a dispersion of a pigment in a fatty oil on said photoconductive layer before or directly after exposure, said fatty oil being at least partially liquid at a temperature of from normal temperature to about 40 C.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to an improved process for electrophotography and more prarticularly to a process for converting latent images, formed on a photoconductive layer as a pattern of differing electro-conductivity, into visible images by electrolytic development.

(2) Description of the prior art There is known a reproduction process in which a photoconductive layer consisting of photoconductive powders, such as, photoconductive zinc oxide powders uniformly dispersed in an insulating resin or binder, is formed on an electro-conductive base plate. The layer is exposed imagewise to form latent images by the difference in electro-conductivity, and simultaneously or directly after exposure the layer having the latent images is subject to electrolysis in an electrolyte bath containing therein a material capable of forming visible images on the layer by an oxidation or reduction under a DC. electric field, whereby the electrolytic reaction progresses on the layer in conformity with the paterns of electro-conductivity to provide visible images. In the most general embodiments of this kind of reproduction process, as the material to be incorporated in the electrolyte bath, there are usually employed metal salts capable of forming colored metallic images by reduction, such as, silver nitrate, nickel chloride, copper sulfate, and the like. Organic compounds capable of forming colored image by reduction are also employer in the electrolyte bath. As the photoconductive layer, there is employed a layer containing a large amount of zinc oxide powders as the photoconductive material.

In other embodiments of the foregoing system, a compound, such as indium oxide is incorporated in the photoconductive layer alone or together with zinc oxide and only the salt of a comparatively basic metal is incorporated in the electrolytic bath, whereby at electrolysis the indium ions in the photoconductive layer are reduced to provide visible images.

Also, there is still another embodiment in which a layer containing a hydrophilic binder, such as, gelatin, and a water-soluble metal salt capable of providing metal- Patented Feb. 23, 1971 "ice lie images by reduction, together with another electrolyte, is formed on or applied to the surface of a photoconductive layer.

There are various processes for obtaining color prints or reproductions by using the aforesaid electrolytic electrophotography, but the results are not always satisfactory in regard to the light resistance, color hue, density, etc., of the colored images or dye images thus obtained. Furthermore, in the known processes, the materials employed are generally expensive.

Therefore, an object of this invention is to provide a novel electrolytic electrophotographic process which is not accompanied by the above-mentioned disadvantages.

Another object of this invention is, to provide an improved electrolytic electrophotographic process without the need of using the usual electrolytic developer which becomes unstable in course of time.

Still another object of this invention is to provide an improved electrolytic electrophotographic process capable of easily obtaining a reproduction from a positive original.

SUMMARY OF THE INVENTION The inventors have found, as the result of investigations for overcoming the aforesaid disadvantages, that colored images having high light resistance and a clear color hue can be obtained by forming an oil layer containing a pigment or a coloring matter on the surface of a photoconductive layer and subjecting the layer to electrolysis in an electrolyte bath.

The above stated and other objects of the present inventon can be attained by the present invention. That is, according to the present invention, in a process of forming visible images by exposing imagewise a photoconductive layer comprising a photoconductive material, such as, photoconductive zinc oxide powders and a binder formed on a conductive base plate to form in the layer latent image by the patterns of electroconductivity and subjecting simultaneously or directly after exposure, said layer to electroylsis in an electrolyte by passing an electric current selectively through the thus exposed areas of the layer, there is formed on or applied to the surface of the aforesaid photoconductive layer a dispersion of a pigment in a fatty oil which is at least partially liquid at temperatures in the range of from normal temperature to 40 C., does not attack the light-sensitive material, and is substantially non-volatile in the temperature range.

DETAILED DESCRIPTION OF THE INVENTION Now, the invention will be explained in detail.

The light-sensitive or photoconductive layer of the photoconductive element used in this invention may be the same as that for usual electrolytic electrophotography. That is, the photoconductive element used in this invenion maybe prepared by forming a photoconductive layer comprising photoconductive zinc oxide powders and an electrically insulative binder on a support having proper mecahnical properties. However, since an electric potential must be applied for conducting the electrolysis, at least the surface of the support in contact with the photoconductive layer must be highly conductive. Accordingly, in the case where the support is of plastic or glass, a thin layer of a metal, such as aluminum must be formed on the surface thereof.

In the latter case, a vacuum deposited film of aluminum is usually employed as the thin film of a metal. However, there may be employed other conductive supports, such as, one of the so-called conductive glasses having a thin film of a conductive oxide thereon, e.g., tin oxide, a carbon black-containing paper, a paper containing fine metallic filaments, a paper containing glass fibers on which a metal has been deposited by a nonelectrolytic plating method, and a paper on the surface of which an aluminum foil has been attached. Of course, the use of metallic plates is preferable.

The photoconductive or light-sensitve layer comprises a uniform mixture of photoconducitve material, such as, photoconductive zinc oxide powders, and a binder having a high electric resistance. As the photoconductive zinc oxide, one prepared by the French method is preferable As the photoconductive material, there may of course be employed, besides zinc oxide, cadmium sulfide, selenium, organic photoconductive materials, etc.

The properties of the photoconductive element are largely influenced by the properties of the binder which is employed. The most preferable example of a binder is a copolymer of syrene and butadiene, one of which is commercially available under the Pliolite S-SD and -7 mark (trade name of Goodyear Tire & Rubber Go). Other binders which may be used in this invention are polyepoxy ester of an aliphatic acid, a copolymer of vinyl chloride and vinyl acetate, polyvinyl acetate and the like. If necessary, there may be incorporated in the binder, a plasticizer, another photoinactive pigment, and a lubricant. A surface active agent may, of course, be used to adjust the coating properties or wetting properties of the coating composition of the photoconductive layer. Further, since the light-sensitive region of Zinc oxide is in the region of violet to blue, the light-sensitive region thereof may be enlarged by the addition of a sensitizing dye. A small amount of other various sensitizing materials may be incorporated.

The main feature of the present invention is the forming on the surface of the photoconductive layer of the photoconductive element a layer comprising a dispersion of a pigment in a fatty oil which is at least partially in the liquid state at a temperature in the range of from room temperature to 40 C., and does not attack the lightsensitive or photoconductive element and is substantially non-volatile in this temperature range.

As the liquid organic materials, there are preferably illustrated vegetable oils, such as, linseed oil, cotton seed oil, soybean oil, sesame oil, castor oil, rapeseed oil, hemp seed oil, tung oil, walnut oil, and the like and animal oils, such as, shark liver oil, sardine oil, cod liver oil, whale oil, beef tallow, lard and the like.

Some of these fatty oils may dissolve the binder used in the photoconductive or light-sensitive layer or have miscibility with the binder and hense When the lightsensitive or photoconductive element having the photoconductive layer is allowed to stand for a long period of time, the surface layer containing the organic material will be diffused in the photoconductive layer. However, as will be understood from the nature of the organic material, the process of this invention will be finished in a very short period of time, as compared with the time required to cause the aforesaid trouble. Hence, even in such a case, the layer of the dispersion formed on the photoconductive layer may be regarded as a separated surface layer. However, if the surface layer thus formed shall be completely diffused in the photoconductive layer, the merits of this invention are not obtained.

The application of such an organic material to the surface of the photoconductive layer has the additional merit that the formation of hydrogen foam on the surface of the photoconductive layer at electrolysis is suppressed, whereby the formation of development unevenness can be removed. Further, it has the merit that pin holes caused by the low insulating property, if any, is partially present on the photoconductive layer, can be covered by the dispersion.

Since the oil layer of the dispersion has low electric conductivity, the thickness of the layer is preferably less than microns. Moreover, since some of the aforesaid oils have unsaturated bonds, they can be cured in the course of time or by applying a proper processing to the oil, as for example, by hydrogenation of the oil or by the use of curing agents, etc.

As the pigments or coloring matter to be dispersed in the fatty oil, there may be employed various inorganic and organic pigments. For example, as inorganic pigments to be employed in this invention, there are illustrated carbon black, ultramarine blue, cadmium yellow, red oxide, titanium white, and the like and as the organic pigments there are illustrated azo pigments, triphenylmethane pigments, quinoline pigments, anthraquinone pigments, phthalocyanine pigments and the like. These pigments may preferably be incorporated in the organic material or the aforesaid fatty oil in an amount of 5-40 parts by weight based on parts by weight of the fatty oil. The use of a kneader usually employed in the. ink-manufacturing industry is preferably for preparing the dispersion. In this case, to facilitate the dispersion of pigments, a suitable additive may be used or the pigments may be subjected to surface treatment. Furthermore, various commercially available printing inks may be mixed in the fatty oil.

If the dispersion of the pigment in the fatty oil has a large absorption in the spectrally sensitive region of the photoconductive light-sensitive layer, the layer of the dispersion may be formed thereon after exposure, but if the layer has a low absorption, the dispersion layer may be formed on the surface of the photoconductive light-sensitive layer before exposure.

As known in the art, if the conductive support is transparent such as a glass support having a tin oxide layer thereon, the opaque dispersion layer can be formed on the surface of the photoconductive layer before exposure. In this case the photoconductive layer is exposed to the image through the glass support.

The electrolyte bath used in this invention is generally one prepared by dissolving an electrolyte in water. For example, an alkali metal salt may be dissolved in water. An electrolyte bath containing a water-soluble heavy metal salt gives no preferable results since the metal tends to deposit on the exposed portions of the photoconductive layer. An ammonium salt may be employed as the electrolyte in this invention.

The mechanism of the process of this invention has not yet become clear, but it is considered that upon electrolysis, the fatty oil which comprises a glycerine ester of an aliphatic acid is attacked by alkali locally formed at the exposed portions, and becomes water soluble, whereby the pigment contained in the fatty oil is dissolved in the electrolyte at the exposed portion.

The invention is described further by the following examples.

EXAMPLE 1 G. Phthalocyanine blue 0.5 Non-ionic surface active agent 0.01 Linseed oil 5 Thereafter, the sample having the dispersion layer was immersed in an aqueous solution of 1 mol of sodium chloride, and a DC. electric current of 1.8 volts applied to a Pt anode and the aluminum plate as the cathode. After continuing the electrolysis for 30 seconds, the sample was withdrawn from the bath to provide a blue negative image.

EXAMPLE 2 Para red 0.8 Soybean oil 4 When the sample was processed, as in Example 1, a red positive image was obtained.

EXAMPLE 3 The same procedure as in Example 1 was repeated while using as the electrolyte bath an aqueous solution of one mol of ammonium chloride and almost the same results were obtained.

EXAMPLE 4 The same procedure as in Example 1 was repeated while using the dispersion having the following composition:

Parts Plano blue (trade name of an otfset ink sold by Fuji Photo Film Co.) 1 Soybean oil 2 and after processing, almost the same results were obtained.

What we claim is:

1. In an electrolytic electrophotographic process involving the steps of exposing a photoconductive layer comprising a photoconductive material and an insulating binder formed on an electrically conductive base plate to form therein a latent image due to the difference in electric conductivity, and subjecting the photoconductive layer having the latent image to electrolysis in an aqueous electrolyte bath to form visible images on the layer, the improvement which comprises forming a layer of a dispersion of a pigment in a fatty oil on said photoconductive layer before or directly after exposure, said fatty oil being at least partially liquid at a temperature of from normal temperature to about C.

2. The electrolytic electrophotographic process as claimed in claim 1 wherein said photoconductive material is photoconductive zinc oxide powder, said layer of dispersion of a pigment in a fatty oil having a thickness of less 10 microns.

3. The electrolytic electrophotographic process as claimed in claim 1 wherein said fatty oil is selected from the group consisting of linseed oil, cotton seed oil, soybean oil, sesame oil, castor oil, rapeseed oil, hemp seed oil, tung oil, and walnut oil.

4. The electrolytic electrophotographic process as claimed in claim 1 wherein said fatty oil is selected from the group consisting of shark liver oil, sardine oil, cod liver oil, whale oil, beef tallow, and lard.

References Cited UNITED STATES PATENTS 3,165,458 1/1965 Harriman 204-18 GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant Examiner US. Cl. X.R. 

